The purpose of this research is to obtain basic structural, genetic, and biological information on a novel mouse T cell differentiation antigen (BM100). Initial findings using a monoclonal antibody to screen normal and neoplastic cells suggest that BM100 is T cell specific except that it is found on a high pecentage of bone marrow cels. Based on this finding it appears that BM100 is present on pre-T cells. This hypothesis will be examined by a combination of techniques including flow cytometry, immunoblots, and bone-marrow chimeras. Structural information on the protein will be obtained using immunoblots, lectin columns, radiolabelling, and one and two dimensional gel analysis. The cDNAs encoding the BM100 antigen will be isolated from a T cell tumor using a cDNA exprssion vector lambda gt11. These clones will be sequenced and used in genetic mapping studies. They will also be used to isolate and characterize genomic clones. The BM100 is interesting since it may represent the earliest marker of T lineage cells. The BM100 is also interesting since it may represent the mouse homolog of a human antigen (gpL115). The gpL115 molecule has recently been found to be altered in patients with Wiskott-Aldrich Syndrome, an X-linked immunodeficiency disorder, which among other defects has T cell abnormalities and often leads to lymphoreticular malignancies.